The present application is a U.S. national stage application of PCT/IL97/00176, filed Jun. 3, 1997.
The present invention relates to improved intermediate transfer blankets, especially suited for transfer of liquid toner images, and methods of producing such blankets.
The use of an intermediate transfer member in electrostatic imaging is well known.
Various types of intermediate transfer members are known and are described, for example in U.S. Pat. Nos. 3,862,848, 4,684,238, 4,690,539 and 4,531,825 and PCT publications WO 96/14619 and WO 97/07433, the specifications of all of which are incorporated herein by reference.
Belt-type intermediate transfer members for use in electrophotography are known in the art and are described, inter alia, in U.S. Pat. Nos. 3,893,761, 4,684,238 and 4,690,539, the specifications of all of which are incorporated herein by reference.
The use of intermediate transfer members and members including transfer blankets, for offset ink printing, is also well known. Such blankets have characteristics which are suitable for ink transfer but they are generally not usable, per se, for liquid toner imaging.
Multi-layered intermediate transfer blankets for toner imaging are known in the art. Generally, such blankets include a thin, multi-layered, image transfer portion and a base (or body) portion which supports the image transfer portion and provides the blanket with resilience during contact with an imaging surface and/or a final substrate. While the process for producing the image transfer portion is a relatively clean process, the base portion is generally not compatible with such clean processes.
One important characteristic of an intermediate transfer blanket is its image release properties. Many of the above referenced publications describe intermediate transfer blankets which are coated with a laver of release material, for example a silicone release layer.
WO 97/07433 describes, inter alia, a release coating comprised of a condensation type silicone material. Condensation type silicones give good release properties and other print quality advantages when used as the release layer for an intermediate transfer blanket. However, the standard catalyst systems are either two slow for useful in-line curing in continuous coating systems or cure so quickly and have no practical pot life. WO 97/07433 also describes a method of constructing an intermediate transfer blanket in which a transfer portion is laminated to a base portion to form the transfer member.
Condensation type silicon curing systems can be used to provide a thin film, as known in the art. Such systems provide very thin films for coating paper and the like with a release coating. However, such silicone materials (which appear to be based on methyl hydrogen cross-linkers) are not suitable for release coating for intermediate transfer blankets, since they do not have the abrasion resistance or the mechanical integrity required. Furthermore, they cannot easily be used to produce a release coating having the thickness required for an intermediate transfer member. For example, one such prior art material SS4191A release coating system (GE) is normally used with a low solids concentration (5%) in order to achieve the thin coating required for paper. When the material was concentrated, the pot life was limited so that it is not suitable for a continuous coating process.
It is an object of one aspect of the present invention to provide a method of coating an object, in particular a image transfer blanket or other intermediate transfer member in which the coating components have a relatively long, stable, pot life on the one hand but a very rapid cure on activation on the other.
The basis of this aspect of the invention is to separate the catalyst and polymer solutions used in forming the release layer and applying them successively to a blanket base. Preferably, the coating process is performed at two stations in a continuous coating system. As long as the two components are separated, the pot life of each material is very long. As soon as the components are brought into contact at the second coating station, a very rapid reaction occurs, preferably facilitated by heat. This allows for coating the bianket base continuously, in a practical manner.
The advantages of continuous coating include improved uniformity, repeatability, controllability and reduced manufacturing costs.
Few (if any) condensation type silicone rubbers exist with the unique combination of long pot life (hours) and rapid cure ( less than 1 minute at 100xc2x0 C.) for thin films (4-5 micron dry film thickness). Furthermore, the disclosed preferred system can be coated and cured onto various types of rubber (acrylic, nitrile), which would normally inhibit and prevent cure in addition-type silicone rubbers.
Preferably, the catalyst solution includes a primer or adhesive to aid adhesion to the underlying rubber, so that cure and adhesion are obtained simultaneously. The preferred silicone and catalyst solutions are optimized to provide improved print quality, ink release, abrasion resistance, long lifetime and good adhesion to an underlying rubber layer. Preferably, the catalyst should also include an additive to improve film forming. One suitable additive is silica.
In a second aspect of the invention, a conforming layer is laminated to the base portion of the intermediate transfer member and a release layer, preferably one produced according to the first aspect of the invention, is coated onto the conforming layer.
There is therefore provided in accordance with a preferred embodiment of the invention, a method of producing a coating on a member comprising:
providing a body portion;
coating the body portion with a catalyst material for a release coating material; and
overcoating the catalyst material with an uncured polymer material for which the catalyst is active. Preferably, the release coating material is a condensation type silicone. Preferably, the silicone comprises a combination of two different silicone materials. Alternatively or additionally, the release coating material utilizes an alkoxy silane cross linker.
Alternatively or additionally, the catalyst coating comprises an adhesion promoter which promotes the adhesion of the cured coating to the body portion. Preferably, the adhesion promoter comprises a silane based primer. Further preferably, the adhesion promoter comprises (3-glycidoxypropyl) trimethoxysilane.
Alternatively or additionally, the body portion comprises a conforming layer on which the catalyst material is coated. Alternatively or additionally, the catalyst material comprises stannous octoate. Additionally or alternatively, the coating comprises a release coating.
In a preferred embodiment of the invention, the member is an intermediate transfer member for toner images. Preferably, the toner comprises a liquid toner.
In a preferred embodiment of the invention the catalyst coating comprises silica.
In a preferred embodiment of the invention, the coating is formed in a continuous coating process.
There is also provided in accordance with a preferred embodiment of the invention, a method of producing a cured condensation type silicone material, comprising:
providing an uncured material; and
adding a stannous octoate catalyst.
There is also provided in accordance with a preferred embodiment of the invention, an intermediate transfer blanket coated with a condensation type silicon material produced by the above method.
There is provided in accordance with another preferred embodiment of the invention a method of producing a coating on an intermediate transfer member comprising:
providing a blanket body portion in web form; and
coating the blanket body portion with a condensation type silicone release layer using a continuous coating process.
Preferably, the intermediate transfer member is an intermediate transfer member for toner images. Further preferably, the toner comprises liquid toner.
In a preferred embodiment of the invention, the release layer utilizes an alkoxy silane cross-linker.
There is also provided in accordance with a preferred embodiment of the invention, an intermediate transfer blanket produced by the above methods.
There is provided in accordance with another preferred embodiment of the invention an intermediate transfer blanket, in web form, coated with a release coating of condensation type silicon.
There is also provided in accordance with a preferred embodiment of the invention, an intermediate transfer blanket comprising:
a release layer; and
an underlayer, comprising stannous octoate, beneath the release layer. Preferably, the release layer comprises dibutyltin dilaurate.
Alternatively or additionally, the underlayer comprises silica. Additionally or alternatively, the underlayer comprises a silane primer.
There is provided in accordance with another preferred embodiment of the invention, an intermediate transfer blanket comprising:
a release layer; and
an underlayer, comprising a silane primer, beneath the release layer. Preferably, the underlayer comprises silica
Alternatively or alternatively, the release layer comprises oleic acid.
There is also provided in accordance with a preferred embodiment of the invention, an intermediate transfer blanket comprising:
a release layer, comprising oleic acid; and
an underlayer beneath the release layer. Preferably, the release layer comprises dibutyltin dilaurate.
Alternatively or additionally, the underlayer comprises silica. Alternatively or additionally, the underlayer comprises a silane primer. Alternatively or additionally, the underlayer comprises stannous octoate.
There is also provided in accordance with a preferred embodiment of the invention; an intermediate transfer blanket comprising:
a polymerized release layer; and
an underlayer beneath the release layer, wherein the underlayer comprises a fast catalyst for forming the release layer and the release layer comprises a slow catalyst for forming the release layer.
Preferably, the release layer comprises an inhibitor for the slow catalyst.
In a preferred embodiment of the invention, the release layer is a condensation type release layer.